In the case of a gas chromatograph mass spectrometer (GC/MS) or a liquid chromatograph mass spectrometer (LC/MS), sample components which have been temporally separated by a column of a GC or an LC are introduced in sequence into the mass spectrometer (MS), and each component is ionized, respectively, and thereafter subjected to mass separation and detection. In this case, a mass spectrum can be created by focusing on a specific time, and assigning the mass to the horizontal axis and the intensity to the vertical axis. Further, a chromatogram (mass chromatogram) can be created by focusing on a specific mass, and assigning the time to the horizontal axis and the intensity to the vertical axis. Still further, a three-dimensional chromatogram can also be created by combining these and adopting the time, the intensity (ion intensity) and the mass as the three axes.
As the mass spectrometer (MS) for such GC/MS and LC/MS, MSn (where n is an integer equal to or larger than two) mass spectrometers that fragment ions having a specific mass as precursor ions and mass analyze product ions generated by the fragmentation are sometimes used. The MSn mass spectrometers include a mass spectrometer equipped with an automatic MSn analysis function that automatically selects precursor ions based on the results of MSn−1 analysis and performs MSn analysis (for example, refer to JP 2010-19655 A).
In a GC/MS or LC/MS in which such a mass spectrometer having an automatic MSn analysis function is used, for example, a chromatogram or chromatograms on one or a plurality of masses is progressively created while continually introducing the eluate from the column of the GC or LC and repeatedly performing MS (=MS1) analysis. Then, at a point in time at which a signal intensity in the chromatogram satisfies a predetermined condition, for example, a point in time at which the signal intensity exceeds a predetermined threshold as indicated by t1 and t2 in FIG. 6, ions having a mass corresponding to the chromatogram or chromatograms are collected as precursor ions and MS/MS analysis is performed. In order to obtain MS/MS spectra with a high S/N ratio, it is preferable to collect as large amount of precursor ions as possible. For that purpose, a method is available, as shown in FIG. 7, in which precursor ions are collected after a peak top of a chromatogram appears since exceeding the threshold.